The overall aim of this project is to investigate the mechanisms by which the pluripotential hemopoietic stem cell gives rise to macrophages and to characterize the humoral factors involved in this process. Studies supported by the first year of this grant have concerned the structure and function of the mononuclear phagocyte lineage specific growth factor CSF-1. CSF-1 has been shown to consist of two disulfide, 14,000-molecular weight polypeptide chains that are possibly identical. The dimeric protein core is heavily glycosylated with N-linked oligosaccharides of the acidic "complex" type. More than 85% of the carbohydrate can be removed without loss of biological, receptor-binding or antibody-linking activities. However, mild reduction in the absence of dissociating agents results in loss of these activities. These properties of CSF-1 are shared by both murine and human forms of the molecule.